阅读说明：本技术 一种三氧化硫三甲胺中三氧化硫含量的测定方法 (Method for measuring sulfur trioxide content in sulfur trioxide trimethylamine ) 是由 蔡西武 李艳玲 陈晓荔 毕爱莲 严孝红 徐国芹 谢楠楠 杨利 于 2021-07-23 设计创作，主要内容包括：本发明提供了一种三氧化硫三甲胺中三氧化硫含量的测定方法,可有效地避免三氧化硫的损失,去除三甲胺对三氧化硫检测的干扰,且操作简便、线性好、重复性好、溶液稳定。(The invention provides a method for measuring the content of sulfur trioxide in trimethylamine trioxide, which can effectively avoid the loss of sulfur trioxide, remove the interference of trimethylamine on the detection of sulfur trioxide, and has the advantages of simple and convenient operation, good linearity, good repeatability and stable solution.)

1. A method for measuring the content of sulfur trioxide in trimethylamine trioxide is characterized by comprising the following steps:

(1) precisely weighing sulfur trioxide trimethylamine, placing the weighed trimethylamine into an iodine measuring flask which is precisely added with an acid solution in advance, adding water, sealing and shaking to dissolve the trimethylamine;

(2) precisely adding alkaline solution, shaking, boiling, detecting with wet test paper until the steam shows no alkalinity, cooling, and adding water;

(3) adding an indicator solution, titrating by using an acidic titration solution until the solution changes color, and correcting the titration result by using a blank test;

(4) calculating to obtain SO in the sulfur trioxide trimethylamine according to the following formula₃Content (c);

in the formula: v₁Consuming the volume (ml) of acidic titration solution for a blank;

V₂consuming a volume (ml) of acidic titration solution for the sulfur trioxide trimethylamine;

f is the ratio of the concentration value of the acidic titration solution to the nominal value thereof;

m is the amount of sulfur trioxide equivalent to each 1ml of the acidic titration solution;

w is the weighed amount (g) of the sulfur trioxide trimethylamine.

2. The method according to claim 1, wherein in step (1), H is in an acidic solution⁺The molar ratio of the concentration to the sulfur trioxide trimethylamine is 0.6-4.2: 1.

3. The method according to claim 1, wherein in the step (1), the acidic solution is a hydrochloric acid or sulfuric acid solution.

4. The method according to claim 1, wherein in the step (2), the molar ratio of the alkaline solution to the sulfur trioxide trimethylamine is 2.7-18.1: 1.

5. The method according to claim 1, wherein in the step (2), the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

6. The method of claim 1, wherein in step (2), the test strip is a pH strip or a litmus red strip.

7. The method according to claim 1, wherein in the step (3), the acidic titration solution is hydrochloric acid or sulfuric acid titration solution.

8. The method according to claim 7, wherein in the step (3), the hydrochloric acid titration solution is 0.1mol/L or 0.2 mol/L.

9. The method according to claim 7, wherein in the step (3), the sulfuric acid titration solution is 0.1mol/L or 0.05 mol/L.

1. Field of the invention

The invention belongs to the technical field of pharmaceutical analysis, and particularly relates to a method for measuring the content of sulfur trioxide in trimethylamine trioxide.

2. Background of the invention

Sulfur trioxide (SO)₃) Is easy to absorb waterIn addition, the smoke is strongly produced in the air, and the sulfuric acid is generated and releases a large amount of heat when dissolved in water. Sulfur trioxide is a strong oxidizing agent commonly used as an organic oxidizing agent and as a sulfuric acid esterifying agent. The direct sulfation of alcoholic and phenolic hydroxyl groups with liquid or gaseous sulfur trioxide often involves a number of problems, such as polymer formation and sulfur trioxide treatment. Therefore, sulfur trioxide is usually subjected to sulfation after forming a complex with an amine, an amide, an ether or the like (advances in the study of the thioaromatization of valet's Arbitol. university, proceedings of southeast university (medical edition), 2010, Dec; 29(6): 707-710). The compound of sulfur trioxide and amine has wide application in sulfation.

The sulfur trioxide trimethylamine is a compound of sulfur trioxide and trimethylamine, the CAS number is 17736-86-6, and the molecular formula is C₃H₉N·O₃S, molecular weight 139.17. The sulfur trioxide trimethylamine has mild reaction and stable property, and has important effect in the field of pharmacy. For example, in the preparation of key intermediates of an antithrombotic drug fondaparinux sodium and an antibacterial drug avibactam sodium, the sulfur trioxide trimethylamine is used as a sulfating agent of hydroxyl, and the quality condition of the sulfur trioxide trimethylamine plays an important role in the preparation of the drug intermediates.

The sulfur trioxide is used as a main active ingredient of the sulfur trioxide trimethylamine to participate in chemical reaction, and is a key factor for determining the performance of the sulfur trioxide trimethylamine. Therefore, controlling the sulfur trioxide content in the sulfur trioxide trimethylamine is of great importance.

At present, no relevant documents and reports of a method for detecting the content of sulfur trioxide in the trimethylamine trioxide are found, and the method for detecting the content of sulfur trioxide needs to be developed in order to enhance the quality control of the trimethylamine trioxide.

3. Summary of the invention

The invention aims to solve the problems in the prior art and provides a method for detecting the content of sulfur trioxide in trimethylamine trioxide, which is simple and convenient to operate, good in linearity, good in repeatability and stable in solution, so as to meet the existing requirements.

The invention provides a method for measuring the content of sulfur trioxide in trimethylamine trioxide. The method comprises the following steps:

(1) precisely weighing sulfur trioxide trimethylamine, placing the weighed trimethylamine into an iodine measuring flask which is precisely added with an acid solution in advance, adding water, sealing and shaking to dissolve the trimethylamine;

(2) precisely adding alkaline solution, shaking, boiling, detecting with wet test paper until the steam shows no alkalinity, cooling, and adding water;

(3) adding an indicator solution, titrating by using an acidic titration solution until the solution changes color, and correcting the titration result by using a blank test;

(4) calculating to obtain SO in the sulfur trioxide trimethylamine according to the following formula₃Content (c);

in the formula: v₁Consuming the volume (ml) of acidic titration solution for a blank;

V₂consuming a volume (ml) of acidic titration solution for the sulfur trioxide trimethylamine;

f is the ratio of the concentration value of the acidic titration solution to the nominal value thereof;

m is the amount of sulfur trioxide equivalent to each 1ml of the acidic titration solution;

w is the weighed amount (g) of the sulfur trioxide trimethylamine.

In the step (1), the acidic solution is a hydrochloric acid or sulfuric acid solution; h in acidic solution⁺The molar ratio of the concentration to the sulfur trioxide trimethylamine is 0.6-4.2: 1, preferably 0.6-2.8: 1.

In the step (2), the alkaline solution is a sodium hydroxide or potassium hydroxide solution; the molar ratio of the alkaline solution to the sulfur trioxide trimethylamine is 2.7-18.1: 1, preferably 5.5-7.0: 1; the detection test paper is pH test paper or litmus red test paper; adding alkaline solution, boiling, and optionally adding water.

In the step (3), the indicator solution is methyl red-bromocresol green indicator solution, methyl red indicator solution or bromocresol green indicator solution; the acid titration solution is hydrochloric acid or sulfuric acid titration solution, the hydrochloric acid titration solution is 0.1mol/L or 0.2mol/L, and the sulfuric acid titration solution is 0.1mol/L or 0.05 mol/L; said calculating SO₃The content method comprises the steps of detecting the amount of alkali in the boiled solution by using an acid titration solution, and calculating the difference value of titration results of the test solution and the blank solution, namely the amount of alkali consumed by sulfuric acid generated by sulfur trioxide, so as to obtain the amount of the sulfur trioxide.

The invention provides a method for measuring the content of sulfur trioxide in trimethylamine trioxide. The method comprises the following steps:

(1) precisely weighing about 0.1g of sulfur trioxide trimethylamine, placing the weighed materials into an iodine measuring flask which is precisely added into an acid solution in advance, adding water, sealing and shaking to dissolve;

(2) precisely adding alkaline solution, shaking, boiling, detecting with wet test paper until the steam shows no alkalinity, cooling, and adding water;

(3) adding an indicator solution, titrating by using an acidic titration solution until the solution changes color, and correcting the titration result by using a blank test;

(4) calculating to obtain SO in the sulfur trioxide trimethylamine according to the following formula₃Content (c);

in the formula: v₁Consuming the volume (ml) of acidic titration solution for a blank;

V₂consuming a volume (ml) of acidic titration solution for the sulfur trioxide trimethylamine;

f is the ratio of the concentration value of the acidic titration solution to the nominal value thereof;

m is the amount of sulfur trioxide equivalent to each 1ml of the acidic titration solution;

w is the weighed amount (g) of the sulfur trioxide trimethylamine.

Wherein the content of the first and second substances,

in the step (1), the addition amount of the acidic solution is H⁺The concentration is 0.5 mmol-3 mmol, preferably 0.5 mmol-2 mmol; the acid solution is hydrochloric acid or sulfuric acid solution.

In the step (2), the adding amount of the alkaline solution is 2 mmol-13 mmol, preferably 4-5 mmol; the alkaline solution is sodium hydroxide or potassium hydroxide solution; the detection test paper is pH test paper or litmus red test paper; adding alkaline solution, boiling, and optionally adding water.

In the step (3), the indicator solution is methyl red-bromocresol green indicator solution, methyl red indicator solution or bromocresol green indicator solution; the acid titration solution is hydrochloric acid or sulfuric acid titration solution, the hydrochloric acid titration solution is preferably 0.1mol/L or 0.2mol/L, and the sulfuric acid titration solution is preferably 0.1mol/L or 0.05 mol/L; said calculating SO₃The content method comprises the steps of detecting the amount of alkali in the boiled solution by using an acid titration solution, and calculating the difference value of titration results of the test solution and the blank solution, namely the amount of alkali consumed by sulfuric acid generated by sulfur trioxide, so as to obtain the amount of the sulfur trioxide.

The invention provides a method for measuring the content of sulfur trioxide in trimethylamine trioxide. The method comprises the following steps:

(1) precisely weighing about 0.1g of sulfur trioxide trimethylamine, precisely adding the weighed sulfur trioxide trimethylamine into an iodine measuring flask which is precisely added with 10ml of 0.1mol/L hydrochloric acid solution in advance, adding 20ml of water, sealing, and shaking to dissolve;

(2) precisely adding 10ml of 0.5mol/L sodium hydroxide solution, shaking up, boiling, detecting with wet pH paper until the steam is not alkaline, cooling, and adding 50ml of water;

(3) adding 5 drops of methyl red-bromocresol green indicator solution, titrating with hydrochloric acid titration solution (0.1mol/L) until the solution changes from green to wine red, correcting the titration result with a blank test, and calculating to obtain SO₃And (4) content.

The invention provides a method for measuring the content of sulfur trioxide in trimethylamine trioxide. The method comprises the following steps:

(1) precisely weighing about 0.1g of sulfur trioxide trimethylamine, precisely adding the weighed sulfur trioxide trimethylamine into an iodine measuring flask which is precisely added with 5ml of 0.1mol/L hydrochloric acid solution in advance, adding 20ml of water, sealing, and shaking to dissolve;

(2) accurately adding 8ml of 0.5mol/L sodium hydroxide solution, shaking, boiling, detecting with wet pH paper until the steam is not alkaline, cooling, and adding 50ml of water;

(3) adding 5 drops of methyl red-bromocresol green indicator solution, titrating with hydrochloric acid titration solution (0.1mol/L) until the solution changes from green to wine red, correcting the titration result with a blank test, and calculating to obtain SO₃And (4) content.

The invention provides a method for measuring the content of sulfur trioxide in trimethylamine trioxide. The method comprises the following steps:

(1) precisely weighing about 0.1g of sulfur trioxide trimethylamine, precisely adding the weighed materials into an iodometric flask which is precisely added with 10ml of 0.1mol/L sulfuric acid solution in advance, adding 20ml of water, sealing, and shaking to dissolve;

(2) precisely adding 10ml of 0.5mol/L potassium hydroxide solution, shaking up, boiling, detecting with wet pH paper until the steam is not alkaline, cooling, and adding 50ml of water;

(3) adding 5 drops of methyl red indicator solution, titrating with sulfuric acid titration solution (0.05mol/L) until the solution turns from yellow to red, correcting the titration result with a blank test, and calculating to obtain SO₃And (4) content.

The invention has the beneficial effects that:

(1) the solubility of the trimethylamine trioxide in water is poor, the solubility in hot water and an acidic solvent is good, the solubility can be increased by dissolving a sample in the acidic solvent, and the reaction of the sulfur trioxide and the water is easy to generate sulfuric acid. In order to prevent sulfur trioxide from overflowing under the heating condition, an acid solvent is selected for dissolving, so that the loss of sulfur trioxide can be effectively avoided;

(2) the boiling point of trimethylamine is about 2.75 ℃, and the trimethylamine is easily dissolved in water, and can be boiled out under the alkaline condition; thereby avoiding the interference of trimethylamine during the subsequent acid-base titration;

(3) and (3) titrating the difference value between the alkali and the blank solution by using acid, namely the amount of the alkali consumed by the sulfuric acid generated by sulfur trioxide, so as to obtain the amount of the sulfur trioxide.

(4) The method is simple and convenient to operate, good in linearity, good in repeatability and stable in solution.

In conclusion, the method for measuring the content of sulfur trioxide in the trimethylamine trioxide can effectively avoid the loss of the sulfur trioxide, remove the interference of the trimethylamine on the detection of the sulfur trioxide, and has the advantages of simple operation, good linearity, good repeatability and stable solution.

4. Description of the drawings

FIG. 1 is a graph showing the linear results of the sulfur trioxide content measurement in trimethylamine trioxide in the linear test of example 7.

5. Detailed description of the preferred embodiments

The following detailed description of specific embodiments of the present invention is provided for illustrative purposes only and is not intended to limit the scope of the present invention.

Reagent

Preparing a 0.1mol/L hydrochloric acid solution: 9ml of hydrochloric acid is taken, a proper amount of water is added to make the volume of the hydrochloric acid to be 1000ml, and the mixture is shaken up.

Preparation of 0.5mol/L sodium hydroxide solution: 20g of sodium hydroxide is taken, dissolved in water and diluted to 1000ml, and shaken up.

0.1mol/L sulfuric acid solution: slowly adding 6.0ml of sulfuric acid into a proper amount of water while stirring, cooling to room temperature, adding water to dilute to 1000ml, and shaking up.

Preparation of hydrochloric acid titration solution (0.1 mol/L): 9ml of hydrochloric acid is taken, a proper amount of water is added to make the volume of the hydrochloric acid to be 1000ml, and the mixture is shaken up.

Standardization of hydrochloric acid titration solution (0.1 mol/L): taking 0.15g of anhydrous sodium carbonate dried at 270-300 ℃ to constant weight, precisely weighing, adding 50ml of water for dissolving, adding 10 drops of methyl red-bromocresol green mixed indicating liquid, dripping the liquid until the solution is changed from green to purple, boiling for 2 minutes, cooling to room temperature, and continuously titrating until the solution is changed from green to dark purple. Each lml of hydrochloric acid titrant (0.lmol/L) corresponds to 5.30mg of anhydrous sodium carbonate. And calculating the concentration of the solution according to the consumption of the solution and the consumption of the anhydrous sodium carbonate.

Sulfuric acid titration solution (0.05 mol/L): slowly adding 3.0ml of sulfuric acid into a proper amount of water while stirring, cooling to room temperature, adding water to dilute to 1000ml, and shaking up.

Standardization of sulfuric acid titration solution (0.05 mol/L): and a method for standardizing a titration solution of hydrochloric acid.

Preparing a methyl red-bromocresol green indicating solution: and (3) taking 20ml of 0.1% methyl red ethanol solution, adding 30ml of 0.2% bromocresol green ethanol solution, and shaking up to obtain the compound.

Example 1 Sulfur trioxide content determination

Taking about 0.5g of sulfur trioxide trimethylamine, adding 30ml of water, adding 10ml of hydrochloric acid for dissolving, and sealing. 40ml of barium chloride test solution is dripped to precipitate, the solution is boiled for 2 minutes after being placed for about 30 minutes, and the solution is cooled and kept still for 4 hours. Filter with quantitative filter paper and wash with water until the precipitate is free of chloride ions (checked with silver nitrate test solution). And transferring the precipitate and the filter paper to a porcelain crucible which is burned to constant weight at 800 ℃, ashing, and burning to constant weight at 800 ℃. And (3) calculating the sulfur trioxide content in the sulfur trioxide trimethylamine according to the formula (1).

In the formula: m is₂The weight (g) of the barium sulfate precipitate after ignition;

m₁weighing the amount (g) of trimethylamine trioxide;

80.06 is the molecular weight of sulfur trioxide trimethylamine;

233.39 is the barium sulfate molecular weight.

The content of sulfur trioxide in the trimethylamine trioxide is measured to be about 10.5 percent, the content is low, the loss is caused in the precipitation and washing process, the operation is complicated, the time consumption is long, and the method is not suitable for use.

Example 2 Sulfur trioxide content determination

Taking about 0.1g of sulfur trioxide trimethylamine, precisely weighing, placing into an iodine measuring flask which is precisely added with 10ml of 0.1mol/L hydrochloric acid solution in advance, sealing, shaking up, precisely adding 25ml of 0.1mol/L sodium hydroxide solution for dissolving, extracting for 3 times by using trichloromethane, 10ml each time, discarding an organic phase, washing a separating funnel for 3 times by using water, 5ml each time, and combining an aqueous phase and a washing liquid. 5 drops of methyl red-bromocresol green indicator solution are added, the solution is titrated with hydrochloric acid titrant (0.1mol/L) until the solution changes from green to wine red, and the titration result is corrected by a blank test, wherein each 1ml of hydrochloric acid titrant (0.1mol/L) corresponds to 4.003mg of SO₃. As a result: the solubility of trimethylamine in water is higher than that of the trimethylamine, the trimethylamine interference cannot be removed, the blank titration volume is not different from the sample titration volume, and the method is not suitable for use.

Example 3 Sulfur trioxide contentMeasurement of

Precisely weighing about 0.1g of trimethylamine trioxide, precisely weighing, precisely adding the weighed materials into an iodine measuring flask which is pre-precisely added with 10ml of 0.1mol/L hydrochloric acid solution, adding 20ml of water, sealing, shaking for dissolving, precisely adding 10ml of 0.5mol/L sodium hydroxide solution, shaking evenly, boiling, detecting by using a wet pH test paper until steam shows no alkalinity, cooling, adding 50ml of water, adding 5 drops of methyl red-bromocresol green indicator solution, titrating by using hydrochloric acid titration solution (0.1mol/L) until the solution changes from green to wine red, and correcting the titration result by using a blank test, wherein each 1ml of hydrochloric acid titration solution (0.1mol/L) is equivalent to 4.003mg of SO₃. Two batches of samples of sulfur trioxide trimethylamine (source: Aldrich) were tested and the sulfur trioxide content was calculated according to the following equation.

In the formula: v₁The volume (ml) of hydrochloric acid titration solution (0.1mol/L) was consumed as a blank;

V₂the volume (ml) of hydrochloric acid titration solution (0.1mol/L) was consumed for sulfur trioxide trimethylamine;

f is the ratio of the concentration value of the hydrochloric acid titration solution (0.1mol/L) to the nominal value thereof;

m is the amount of sulfur trioxide equivalent to 0.1mol/L per 1ml of hydrochloric acid titration solution, namely 4.003 mg;

w is the weighed amount (g) of the sulfur trioxide trimethylamine.

The results are shown in Table 1 below.

TABLE 1 results for sulfur trioxide content in trimethylamine trioxide

The results show that: the measured result obtained by the method has good parallelism, and the measured result is close to the theoretical content of the sulfur trioxide of 57.5 percent.

Example 4 Sulfur trioxide content determination

The method of example 2 was used to determine the sulfur trioxide content of different batches of sulfur trioxide trimethylamine.

The results show that the sulfur trioxide content of the two samples of MKBK2211V batches of sulfur trioxide trimethylamine is 56.60% and 56.40%, respectively, and the average value is 56.50%.

Example 5 Sulfur trioxide content determination

Precisely weighing about 0.1g of trimethylamine trioxide, precisely weighing, precisely adding the weighed materials into an iodine measuring flask which is pre-precisely added with 5ml of 0.1mol/L hydrochloric acid solution, adding 20ml of water, sealing, shaking for dissolving, precisely adding 8ml of 0.5mol/L sodium hydroxide solution, shaking evenly, boiling, detecting by using a wet pH test paper until steam shows no alkalinity, cooling, adding 50ml of water, adding 5 drops of methyl red-bromocresol green indicator solution, titrating by using hydrochloric acid titration solution (0.1mol/L) until the solution changes from green to wine red, and correcting the titration result by using a blank test, wherein each 1ml of hydrochloric acid titration solution (0.1mol/L) is equivalent to 4.003mg of SO₃. The sulfur trioxide content was calculated according to the following formula.

In the formula: v₁The volume (ml) of hydrochloric acid titration solution (0.1mol/L) was consumed as a blank;

V₂the volume (ml) of hydrochloric acid titration solution (0.1mol/L) was consumed for sulfur trioxide trimethylamine;

f is the ratio of the concentration value of the hydrochloric acid titration solution (0.1mol/L) to the nominal value thereof;

m is the amount of sulfur trioxide equivalent to 0.1mol/L per 1ml of hydrochloric acid titration solution, namely 4.003 mg;

w is the weighed amount (g) of the sulfur trioxide trimethylamine.

And detecting MKCH1333 batches of the trimethylamine trioxide sample to obtain a result that the content of the sulfur trioxide is 56.83 percent.

Example 6 Sulfur trioxide content determination

Precisely weighing about 0.1g of trimethylamine trioxide, precisely adding into a 10ml iodine measuring flask with 0.1mol/L sulfuric acid solution, adding 20ml of water, sealing, and shaking to dissolveDissolving, adding potassium hydroxide solution 0.5 mol/L10 ml precisely, shaking, boiling, detecting with wet pH paper until the steam is not alkaline, cooling, adding water 50ml, adding methyl red indicator 5 drops, titrating with sulfuric acid titration solution (0.05mol/L) until the solution turns from yellow to red, and correcting the titration result with blank test, wherein each 1ml sulfuric acid titration solution (0.05mol/L) is equal to SO 4.003mg₃. The sulfur trioxide content was calculated according to the following formula.

In the formula: v₁The volume (ml) of sulfuric acid titration solution (0.05mol/L) was consumed as a blank;

V₂the volume (ml) of sulfuric acid titration solution (0.05mol/L) was consumed for the sulfur trioxide trimethylamine;

f is the ratio of the concentration value of the sulfuric acid titration solution (0.05mol/L) to the nominal value thereof;

m is the amount of sulfur trioxide equivalent to 4.003mg per 1ml of sulfuric acid titration solution (0.05 mol/L);

w is the weighed amount (g) of the sulfur trioxide trimethylamine.

And detecting MKCH1333 batches of the trimethylamine trioxide sample to obtain a result that the content of the sulfur trioxide is 56.21%.

Example 7 Linear test

Weighing 0.06g, 0.08g, 0.1g, 0.12g and 0.14g of trimethylamine trioxide, precisely weighing, respectively placing into an iodine measuring flask which is precisely added with 10ml of 0.1mol/L hydrochloric acid solution in advance, adding 20ml of water, sealing, shaking for dissolving, precisely adding 10ml of 0.5mol/L sodium hydroxide solution, shaking uniformly, boiling, detecting by a wet pH test paper until steam is not alkaline, cooling, adding 50ml of water, adding 5 drops of methyl red-bromocresol green indicator solution, titrating by hydrochloric acid titration solution (0.1mol/L) until the solution is changed from green to wine red, and correcting the titration result by a test, wherein each 1ml of blank hydrochloric acid titration solution (0.1mol/L) is equivalent to 4.003mg of SO₃. The volume of the hydrochloric acid titration solution (0.1mol/L) actually consumed is used for plotting the sample weighing amount of the sample, and a regression equation, a correlation coefficient and an intercept are calculated. The results show that: the content of sulfur trioxide in the range of 0.0618-0.1438 g of trimethylamine trioxide is linear, and the specific results are shown in table 2 and fig. 1.

TABLE 2 Linear results for sulfur trioxide content in trimethylamine trioxide

Sample weighing Range (g)	Linear equation of equations	Correlation coefficient	Intercept (%)
				0.0618～0.1438	y＝136.14x+0.0428	0.9999	0.31

EXAMPLE 8 repeatability test

Precisely weighing 6 parts of trimethylamine trioxide about 0.1g, precisely weighing, respectively placing in an iodine measuring flask which is precisely added with 10ml of 0.1mol/L hydrochloric acid solution in advance, adding 20ml of water, sealing, shaking for dissolving, precisely adding 10ml of 0.5mol/L sodium hydroxide solution, shaking uniformly, boiling, detecting with a wet pH test paper until the steam is not alkaline, cooling, adding 50ml of water, adding 5 drops of methyl red-bromocresol green indicator solution, titrating with hydrochloric acid titration solution (0.1mol/L) until the solution is changed from green to wine red, and correcting the titration result with a blank test, wherein each 1ml of hydrochloric acid titration solution (0.1mol/L) is equivalent to 4.003mg of SO₃. The sulfur trioxide content was calculated separately and the relative standard deviation of the contents was calculated. The results show that: sulfur trioxide content in sulfur trioxide trimethylamineThe results of the measurement precision test were good, and the specific results are shown in Table 3.

TABLE 3 measurement of sulfur trioxide content in trimethylamine trioxide precision test results

Serial number	1	2	3	4	5	6	RSD(％)
								Content (%)	56.72	56.38	56.65	56.41	56.53	56.25	0.32

Example 9 solution stability test

Taking about 0.1g of sulfur trioxide trimethylamine, precisely weighing, respectively placing and precisely adding 0.1mol/L hydrochloric acid solution in total 5 partsAdding 20ml of water into a 10ml iodine measuring flask, sealing, shaking for dissolving, precisely adding 10ml of 0.5mol/L sodium hydroxide solution, shaking uniformly, boiling, detecting with a wet pH test paper that the steam is not alkaline, cooling, adding 50ml of water, standing at room temperature for 8 hours under natural light, taking one portion at 0, 2, 4, 6 and 8 hours respectively, adding 5 drops of methyl red-bromocresol green indicator, titrating with hydrochloric acid titration solution (0.1mol/L) until the solution changes from green to wine red, and correcting the titration result with a blank test, wherein each 1ml of hydrochloric acid titration solution (0.1mol/L) is equivalent to 4.003mg of SO₃. The sulfur trioxide content is calculated and the change value of the sulfur trioxide content is calculated respectively. The results show that: the solution of the test sample is stable within 8 hours when the content of sulfur trioxide in the trimethylamine is measured under room temperature natural light. The specific results are shown in Table 4.

TABLE 4 stability test results of test solutions for determining sulfur trioxide content in trimethylamine trioxide

Time (hours)	0	2	4	6	8	Maximum change value (%)
							Content (%)	56.72	56.36	56.78	56.30	56.71	0.42